The state of natural radionuclides of uranium, radium, and thorium in soils

A review of publications is presented on the state of uranium, radium, and thorium in soils. It is shown that the properties of radionuclides in soils provide the diversity of the forms and mechanisms of their fixation in the soil exchange complex. Organic substances and clay minerals are the most important sorbents of uranium, radium, and thorium. According to the available data, the processes of ion exchange, complexing, hydrolysis, and reduction-oxidation are responsible for the uranium and thorium fixation in soils. For radium, the ion exchange and coprecipitation with its chemical macro analogs and iron hydroxides are considered to be the most important. The initial chemical form of the elements and the presence of macrocomponents affect the sorption behavior of radionuclides from technogenic sources. It is emphasized that the current methods of investigation do not allow assessing in full measure the transformation of the forms and the mechanisms of uranium, radium, and thorium fixation in soils. The causes are presented that make the interpretation of the results obtained difficult.